Combustion and halosilane reaction treatment of a formation to increase production



ass-or through an input well or wells.

United rates Donald C. Bond, Crystal Lake, 11]., assignor to The Pure Oil Company, Chicago, 11]., a corporation of Ohio No Drawing. Application November 8, 1954, Serial No. 467,650

6 Claims. (Cl. 16638) The invention relates to a method of increasing the production rates of oil and gas Wells producing fluids containing small amounts of water, and, more particularly, relates to a method of increasing the permeability of earth formation by a first step of dehydrating the formation through controlled combustion of the interstitial oil therein, followed by treatment with a gas containing an organo-silicon compound capable of polymerizing and forming a thin Water-resistant film in the interstices of the formation.

It becomes then a principal object of this invention to provide a process for increasing the permeability of earth formation and preventing the hydration of the formation so treated.

The problem of recovering petroleum or hydrocarbon gases from subterranean formations after substantial depletion of gas pressure, rock pressure, or failure of natural water drive or secondary recovery operations is one of long standing. After pumping fails to recover the oil at an economical rate and secondary recovery operations such as gas drive or water drive no longer are feasible, there still remains a considerable portion of oil or gas in the formations.

It has long been known that by heating underground earth formations, such materials as wax, sulfur, and other deposits can be removed. By using high temperatures, the exposed surfaces of the formations can be spalled off or melted to renew the surfaces of the interior walls of the well bore. Such processes entail merely injecting gaseous or liquid fuel into the well bore, igniting it, forcing air down to support combustion and causing upward circulation of the air therethrough to maintain combustion.

It has been proposed to increase the recovery of the oil by combustion or burning of a part of the oil in place in the reservoir. Such combustion is supported by the continuous injection of air or other oxidizing gas mixtures By these methods, the heat of combustion causes decrease in viscosity of the oil, and initiates distillation and viscosity-breaking to release products which are forced to and recovered from one or more output wells. To initiate such combustion, it has been suggested to place charcoal in the input well adjacent the formation to be treated and ignite the charcoal. This method is not always reliable since combustion is not always uniform and the temperatures attained may be so high in certain areas, that is, up to 2000 to 2500" E, as to cause fusion of the formation with resulting in1pedance of the flow of air to the combustion zone. in certain cases, this type of combustion causes caving or disintegration of parts of the walls of the well-bore cavity so that it is necessary to clean or rebore the well before completing the combustion process. In some instances the burning of the well has been found to result in plugging of the well bore with loose sand where temperatures of 1000 F. or more were attained. Investigators of this problem have suggested the use of a combustible material comprising a mixture of solid combustible coke, coal, or charcoal atent Q ice with a granular refractory material such as sand, stone, pebbles, etc. Mixtures of air, natural gas, and production gas have been used as the injection medium. Dependence is had on the distillation and/ or cracking of the petroleum to allow the products to be forced to an output well for recovery in this method.

These prior art methods of initiating combustion in a well bore are generally conducted without regard to the temperatures attained, irrespective of the type of formation being treated, and have as their primary purpose the propagation of the combustion entirely through the formation, using the combustion to force the oil from the formation to an output well in one form or another. Furthermore, after the flame propagation is completed, the formation is hygroscopic and tends to absorb Water very easily, causing the relative permeability to decrease. In addition, the maintenance of increased permeabilities of the earth formations is also related to the type of fluid which is subsequently to be produced from the formation and prior art processes completely disregard the relationship. There is support for the idea that the oil-wet-tabili-ty of a formation is essential to maximum production, and in contradistinction to this, there are references that teach that decreases in permeability may result as the oil-wettability of a formation increases. If a mixture of oil and Water passes through a treated formation which is waterwettable, it is conceivable that the Water will penetrate and follow the fine interstices while the oil will follow the coarse interstices and, consequently, be produced more rapidly. If this same formation after treatment is made oil-wetta-ble, the Water will tend to pass through the coarse interstices and the oil will become occluded in the finer interstices. Thus, oil-wettability may not be desirable where the amount of Water commingled with the oil is greater than the natural connate water present.

In accordance with copending application entitled Increasing Production Rates of Gas and Oil Wells by D. C. Bond, Serial Number 443,160, filed July 13, 1954, the permeabilities of bentonitic type formations are increased by propagating a flame Within the formation surrounding a well bore under conditions to attain a temperature of between about 200 to 500 C. and thereby irreversibly dehydrate the formation. The practice of this copending application is restricted to those formations which may be irreversibly dehydrated and cannot be applied to hygroscopic formations.

The present invention employs the first step of flame propagation within the formation to dehydrate the formation and leave thereon a small film of Water. This step is followed by the addition of a fluid to said formation for the purpose of preventing its subsequent hydration and making the formation oi-l-wettable. For this latter purpose, a fluid containing organic siloxanes or chlorosilanes or substances polymerizable to organo-siloxanes is used. A principal advantage of this invention is that the process of flame propagation may be extended to formations other than those which are irreversibly dehydrated by heating. As a consequence, there is no necessity to control the rate of combustion as long as a suificiently high temperature is reached to substantially dehydrate the formation and drive out all but a small amount of Water, leaving the surfaces of the interstices capable of reacting with the polymer-forming silicones.

In carrying out the invention, the well to be treated is fitted with a bridge at the top of the oil-sand in which combustion is to be initiated. A casing may be lowered to the bridge by underreaming, and the :well bore is cemented and cleaned. The injection capacity of the well may then be tested. A burner of the type described in United States Patent 2,668,592 is installed. The type of burner used should :be designed to operate with gaseous fuels under injection pressures up to 500 p. s. i. and be able to withstand heat release rates of up to 500,000 B. t. u. per hour. Provision is made for control of burner ignition at the well head and also control of the final combustion temperatures. The burner is placed in the well bore at a point about 8 to 10 feet below the bridge and cement area so as to not expose the casing and cement to direct contact with the combustion area. The well bore is next pressured with air to drive out water and moisture. The combustion material, preferably a mixture of hydrocarbon gases and air, used to initiate the burning may be separately introduced inside the well casing or supplied by a separate conduit. In some instances, a mixture of gaseous combustible material, and air may be injected into the well bore by means of a single conduit and ignited to initiate combustion. A thermocouple is provided, located below the top of the burner, so that observations of the temperature may be made.

Combustion gases with admixed air are then injected and the mixture is ignited by a high-tension spark. Ob-

servations of the temperature are made and, as soon as the thermocouple below the top of the burner indicates a rise in temperature, the gas and .air injection rates are adjusted to give a controlled, hourly, heat-release rate so that the flue gas temperatures are maintained at between about 500 to 600 C. under operating pressure of from 100 to 800 p. s. i. After combustion has been initiated, the injection of the mixture of gas and air is continued at a rate of about 1000 to 2000 cubic feet per day per foot of oil-producing formation being treated. The gasair mixture is adjusted so that it contains from about 2 to 6 percent by volume of oxygen. The temperatures attained within the formation during the heating step should be about 200 C. to about 500 C. and not higher than 600 C. when operating at pressures from 100 to 800 p. s. i. g.

After about 40 to million B. t. u. of heat has been transferred to the formation, the combustion can be transferred to the formation itself by the injection of a noncombustible gas. This creates a heat wave within the formation, and is accomplished by shutting off the fuel gas supply and continuing the injection with air alone. At this point it will be found that the temperature in the combustion chamber will fall but the burning will continue in the earth formation as evidenced by the consumption of oxygen and the appearance of carbon dioxide in the exhaust gases. It will be found expedient to follow the course of the combustion by analysis of the gases taken from an observation .well located a short distance from the combustion well. A mixture of air and hydrocarbon gas having a hydrocarbon content equivalent to about B. t. u./cubic foot and containing about 6 per cent of oxygen is best for causing the combustion to proceed in the formation. Injection of a gas of this composition after the injection of air for a period of about 4 hours may be used to insure that the combustion penetrates the formation. Oxygen contents over about 6 per :cent by volume with an =80 B. it. u. gas are to be avoided since explosive mixtures or flash back may result. The amounts of air and gas are adjusted to provide an amount of oxygen sufficient to stoichiometrically combine with the gas for complete combustion. The injection takes place at pressures from p. s. i. g. to 500 p. s. i. -g., depending on the well-bore pressure which must be overcome. Also, the combustion may be carried out in accordance with United States Patent 2,642,943 provided the temperature limitations of the present invention are followed. I

Injection of the gas is continued until the heat wave has been forced to a distance of 10 to 50 feet from the Well bore. This is accomplished by continuing the injection for a period of from one day to a few weeks. The heat treatment described above is defined to substantially dehydrate the formation, and, under the conditions set forth, there will remain within the interstices of the formation traces of water suflicient for reaction with an organic silicon compound to form therein a water-resistant film. The formation of this water-resistant film is accomplished by treating the formation with an organic silicon compound. For this purpose, a volatile silicon compound is injected into the formation gaseous phase, and in one embodiment of the invention, a halosilane compound or mixtures of one or more of the known halosilanes is introduced in the form of a gaseous media with air or natural gas as the carrier therefor.

There are several types of organosilicon polymers, as for example those involving silicone chains in which two or more silicon atoms bearing organic substituents are attached in any repetitive arrangement, or chains involving silicone-carbon linkages or silicone-oxygen chains, which may be caused to form within the earth formation to form a water-resistant film. These are variously described as siloxane chains, organosilicon polymers or organo-silicon oxides.

Particularly useful resins are those having silicone carbon chains or siloxane chains which constitute a pr. ferred embodiment of the invention. Effective film coatings may be formed in the interstices of the earth formations to make the same water-repellent and oil-wettable by using compounds capable of forming siloxane networks wherein there is a cross-linking of siloxane chains and rings. Cross-linked polymers represent a species having increased average molecular weight-and at the same time three-dimensional networks of increased rigidity and decreased solubility in water. The cross-linking is in reality a condition in which less than two organic substituents are involved per silicon atom so that in the entire polymer the average ratio of alkyl groups to silicon atoms is always less than two. Therefore the R/Si ratio is a convenient measure of the degree of cross-linking. For those polymers having a R/Si ratio of 1.5, it is seen that every other silicon atom (on the average) is crosslinked to another ring or chain. In these polymers where the ratio R/Si equals 1.0, every silicon atom is trifunctional and is bound into a completely cross-linked rigid structure.

One way to form cross-linked polymers is by introducing trifunctional silicon atoms at intervals along the siloxane chains and then establishing oxygen bridges between such monosubstituted trifunctional atoms. Ring structures may be incorporated into the chains.

More specifically, suitable organosilicon compounds may be formed from volatile alkylhalosilanes which are the most useful intermediates for the purpose of forming water-resistant films. These compounds contain an active halogen linkage which is readily converted by hydrolysis into silicols, alkoxysilanes or siloxane polymers and which still retain the organosilicon grouping of the halide. methyl chlorosilane (B. P. 57.6) to tribenzyl chlorosilane are known and available for this purpose. These silicon compounds may be combined with monoand dichloroalkyl silanes or co-polymerized with mixtures thereof to form the so-called silicone resins adapted for use as Well-treating agents by injecting gaseous mixtures of tri-functional silanes and the monoand dichloroalkyl silanes in equal molar proportions.

The method of treating the earth formations in accordance with the second step of the instant invention comprises forcing into the well bore and earth formations being treated, a mixture of the vapors of alkyl silicon halides as methyl silicon chlorides, such as CHsSiClz and .(CH3)2SiCl2. By this treatment the active halogen groups of the methyl silicon chlorides react with available hydrogen and/or hydroxyl groups of the formation or traces of water therein to form waterrepellent films. Illustrative examples of organosilicon halides are: ethyl, propyl-, and butyl silicon halides, the aryl silicon halides, i. e., phenyl silicon halides, aralkyl silicon halides, i. e., tolyl silicon halides and compounds Trialkylchlorosilanes ranging from trisuch as (CH3)zHSiCl, CHsHzSiCl, (CI-I3)3SiCl and the corresponding alkyl aryl halosilanes.

The method described in United States Patent No. 2,469,354 may be used as the second step of the present process. In this method there is incorporated in a gaseous media to be injected into an injection well, such as air, natural gas, or a mixture thereof, a small amount of a substance which hydrolyzes upon contact with moisture to form a hydrophobic solid so that the surface of the formations is not wettable by water but is oil-wettable. Substances suitable for this purpose are the halosilanes having a vapor pressure of at least about 0.001 atmosphere at ordinary temperature including monomethyl dichloromonosilane, dimethyl dichloromonosilane, methyl trichloromonosilane, ethyl trichloromonosilane, propyl trichloromonosilane, diethyl dichloromonosilane, dipropyl dichloromonosilane and methyl ethyl dichlorornoncsilane.

The reservoir conditions of temperature and pressure have been found suitable for the hydrolysis of the halosilanes. In a formation having a temperature of about 150 F. hydrolysis of the halosilanes is completed in 30 minutes to 2 hours. In general, the reaction is rather rapid at temperatures above room temperature and control of the reaction is facilitated by using dilute gaseous solutions of the silicone halosilanes. One aspect of the invention is the discovery that controlled combustion withthe formation at temperatures not exceeding 600 C. renders the formation susceptible to reaction with halosilanes to form a waterresistant film thereon.

A typical example of this invention is as follows: An oil well penetrates a sand section 20 ft. thick, having an average permeability of 100 milidarcies. Combustion is initiated in the well by means of a Piros burner, as described above. After 50 million B. t. u. of heat has been transferred to the formation, the combustion Zone is forced into the rock by injection into the well of a natural gas-air mixture containing 6 per cent oxygen. Injection of this gas is continued for 15 days, at the rate of 250,000 cu. ft. of gas per day. The earth formation will attain a temperature of not over 600 C. and preferably between about 200 to 500 C. Dimethyldichlorosilane is added to all of the injection gas in the proportion of one pound per thousand cu. ft. of gas. The well is then opened to production.

Another aspect of the invention is the treatment of formations containing or producing crude petroleum which has suspended therein about 1.0 per cent or less by volume of connate water. By operating in accordance with the above example the formation is made preferentially oil-wettable and the resistance to flow of the oil to the formation fluids is greatly reduced thereby. The invention is not to be limited to treatment of any particular type of earth formation except that the earth formation should have little tendency to spall or crumble under the heating conditions. Those earth formations such as clay and bentonitic formations, which are irreversibly dehydrated at temperatures above 200 C. in accordance with my copending application, supra, may be advantageously treated in accordance With the present invention. An advantage of the present invention is that the increased permeability attained thereby is longlasting and there is no necessity for the subsequent step of injecting water into the formation to hydrolyze the silicon compounds. Furthermore the inconvenience of using hydrocarbon oil solutions of silicone resins in treating a well is eliminated.

In general the concentration of organic halosilane within the gaseous medium injected into the Well bore may be from about 5 per cent to 10 per cent by volume. This same range of organic halosilane concentration may be applied where mixtures of the methylchlorosilane and dimethylchlorosilane are used.

I claim:

1. The method of increasing the permeability of an earth formation for the purpose of increasing the production of fluids therefrom comprising initiating in a well drilled into said formation, combustion of a combustible material and an oxygen-containing gas, and controlling the content of oxygen in said gas so that the temperature attained within the formation is said well will not be greater than 600 C., continuing said combustion until the formation is heated a substantial depth and thereafter injecting into said formation a gaseous medium containing an organic halosilane to form a Water-resist ant film within the interstices of said formation.

2. The method in accordance with claim 1 in which said combustion is controlled so that the temperature of the earth formation is about 500 C. to thereby condition said formation to be reactable with said organic halosilane.

3. The method in accordance with claim 1 in which the organic halosilane comprises an equimolar mixture of methylchlorosilane and dimethyldichlorosilane capable of forming a cross-linked polymer on hydrolysis and reaction with said formation.

4. The method in accordance with claim 3 in which about 5% to 10% of said mixture of methylchlorosilane and dimethylchlorosilane is present in said gaseous medium comprising a natural gas.

5. The method in accordance with claim 1 in which the gaseous medium contains about one pound of dimethyldichlorosilane per thousand cubic feet of gaseous medium.

6. The method of increasing the permeability of an earth formation for the purpose of increasing the production of fluids containing no more than about 1.0% by volume of connate water therefrom which comprises, initiating in a well bore drilled into said formation, combustion of a combustible material with an oxygen-containing gas, controlling the content of oxygen in said gas so that the temperature attained within the formation is about 500 C. and no greater than 600 0, continuing said combustion until the temperature rise within said formation is extended a radial distance of about 10 to 50 feet from said well bore and thereafter injecting into said formation an equimolar mixture of methylchlorosilane and dimethylchlorosilane in a natural gas, said mixture being capable of forming a cross-linked polymer on hydrolysis and reaction with said formation to form a water-resistant film Within the interstices of said formation.

References Cited in the file of this patent UNITED STATES PATENTS 2,382,471 Frey Aug. 14, 1945 2,469,354 Bond May 10, 1949 2,633,919 Bauer et al Apr. 7, 1953 2,642,943 Smith et a1 June 23, 1953 2,668,592 Piros Feb. 9, 1954 2,670,047 Mayes et al. Feb. 23, 1954 2,685,930 Albaugh Aug. 10, 1954 

1. THE METHOD OF INCREASING THE PERMEABILITY OF AN EARTH FORMATION FOR THE PURPOSE OF INCREASING THE PRODUCTION OF FLUIDS THEREFROM COMPRISING INITIATING IN A WELL DRILLED INTO SAID FORMATION, COMBUSTION OF A COMBUSTIBLE MATERIAL AND AN OXYGEN-CONTAINING GAS, AND CONTROLLING THE CONTENT OF OXYGEN IN SAID GAS SO THAT THE TEMPERATURE ATTAINED WITHIN THE FORMATION IS SAID WELL WILL NOT BE GREATER THAN 600* C., CONTINUING SAID COMBUSTION UNTIL THE FORMATION IS HEATED A SUBSTANTIAL DEPTH AND THEREAFTER INJECTING INTO SAID FORMATION A GASEOUS MEDIUM CONTAINING AN ORGANIC HALOSILANE TO FORM A WATER-RESISTANT FILM WITHIN THE INTERSTICES OF SAID FORMATION. 